This invention relates to a laser scalpel device making use of infrared laser beams which are invisible rays, and more particularly to a focal point direct observation type laser scalpel device having transmission paths for laser beams formed of fibers adapted for infrared rays.
In laser scalpel devices used for surgical operations or laser fabricating devices (hereinafter collectively referred to as "laser scalpel devices"), used for cutting, boring, and joining metallic materials, wooden materials, fabrics and paper, the infrared laser beams, on reaching the end of the transmission path, are injected into the converging lens system and are then converged (focused) at a specific position on the output side of the converging lens system. This position of convergence or focal point constitutes itself the site at which the density of the energy of the infrared laser beams is highest. For this energy to be efficiently used, therefore, the focal point is desired to be capable of being visually recognized by the user or operator of the laser scalpel device.
Since the laser beams are invisible infrared rays, however, the operator is unable to see and tell in advance where the laser beams are focused.
With a view to eliminating this disadvantage, Japanese Patent Application Disclosure Sho 52(1977)-61387 discloses a method for enabling the focal point of laser beams to be recognized by using the infrared laser beams in combination with visible rays. This method utilizes a mirror type guide path for infrared laser beams. The guide path, therefore, causes two visible guide rays to intersect with each other at the focus of a converging lens system on the premise that the focal point of the infrared laser beams coincides with the focus of the converging lens system.
This method, however, has the following drawbacks.
(i) The point at which the two visible guide rays intersect with each other has the highest luminance. The high luminance enables the operator to perceive the focus of the converging lens system but does not permit him to perceive the focal point of the infrared laser beams except in special cases. Generally on the assumption that the image of an object placed at a distance of "a" from a converging lens having a focal distance of "f" is focused at a position separated by a distance of "b" from the aforementioned converging lens, the relation among "a", "b", and "f" is expressed as follows. EQU 1/a+1/b=1/f (1)
In this case, the focus "F" and the focal point "P" coincide with each other when the distance "a" is infinite, namely the incident rays of the converging lens are parallel. This condition occurs only when the transmission path for infrared laser beams is of a junction mirror type. When fibers adapted for infrared rays are used as the transmission path, for example, the distance "a" generally is given a finite value. The device for indicating the focus "F" of the converging lens is utterly meaningless in the laser scalpel device which utilizes fibers adapted for infrared rays as the guide path. Conversely it may prove to be rather harmful in respect that no means is used to indicate the point at which the density of energy is highest.
(ii) Although the device for intersecting two visible guide rays is utilized for the indication of the focus, the intersection of ordinary visible rays cannot produce luminance enough to be visually discerned. For the point of intersection of guide rays to produce sufficient luminance, there must be used guide rays of high directivity. Thus, adoption of visible laser beams is inevitable.
(iii) Since this method relies on the intersection of guide rays to indicate the focus, it is inevitably required to use means for producing two or even more guide rays.
Japanese Patent Application Disclosure Sho 55(1980)-78951 discloses a method which, similarly to the method described above, utilizes a mirror type guide path for infrared rays and, on the premise that the focus and the focal point of infrared laser beams coincide with each other, conducts visible rays through a plurality of optical fibers and causes them to illuminate the focus of infrared laser beams or the surrounding area of the focus. Unfortunately, visible rays departing from optical fibers generally fail to form parallel rays or converging rays. On the contrary, they tend to diverge. For such guide rays to be focused therefore, it becomes necessary to utilize an additional lens to be exclusively used for focusing them. Installation of converging lens at the leading end of each of the plurality of optical fibers, however, adds to the size and complexity of the laser scalpel device and renders the handling of the device difficult.